How to change ink? Experience sharing of UV screen printing matte ink printing

Many plastic color printing factories sometimes need to change ink manufacturers because of ink quality problems, cost, stability and other reasons, but they are more cautious about such problems, fearing that changing ink will affect production, cause reciprocating fluctuations in product quality and cause economic losses to the factory. Different manufacturers will have different ink properties, which will also have different effects on printing.Many plastic color printing factories sometimes need to change ink manufacturers because of ink quality problems, cost, stability and other reasons, but they are more cautious about such problems, fearing that changing ink will affect production, cause reciprocating fluctuations in product quality and cause economic losses to the factory. Different manufacturers will have different ink properties, which will also have different effects on printing.

At present, there are many kinds of inks used in plastic color printing industry, which can be divided into surface Printing Ink and inner printing ink according to the different printing positions. According to the different printing materials, the inner printing ink is divided into polyester nylon ink, OPP special ink and aluminum foil special ink. According to the use temperature, it is divided into ordinary ink, boiled ink, cooking ink and so on. Let's learn how to change the ink, as well as the common problems and solutions of UV screen printing matte ink printing.

Common problems that may be encountered in replacing ink:

1.Hue of ink: Ink is divided into primary color ink and spot color ink. The primary color inks produced by ink manufacturers are all the same, namely, original red, original yellow, original blue, black, white, etc. Spot color inks include ultramarine, scarlet, light yellow, etc. In addition, ink manufacturers will allocate some spot color inks according to the special requirements of customers (generally for printed sheets with large print runs and special patterns).

2.Viscosity of ink: The viscosity of ink produced by different ink manufacturers will be slightly different. After the color printing factory dilutes the ink with mixed solvents, the viscosity of ink is generally controlled between 16 and 26 seconds (No.3 Zahn Cup). Because the printing color sequence and the nature of the ink itself are different, the viscosity required by each ink will be different. Generally, the viscosity of white ink is the lowest, about 17 seconds; The viscosity of black ink is the highest, about 25 seconds, and other colors of ink are between the two.

3.Fineness of ink: the fineness of the same type of ink is generally the same among different ink manufacturers, but the difference between different ink manufacturers lies in the different normal distribution of ink particles, and of course there are other differences. For example, the ink produced by Factory A and the ink produced by Factory B are both between 20 and 28 microns in particle size, but the particle size distribution of ink produced by Factory A is concentrated around 24 microns, while that of ink produced by Factory B is between 20-28 microns.Fineness of ink: the fineness of the same type of ink is generally the same among different ink manufacturers, but the difference between different ink manufacturers lies in the different normal distribution of ink particles, and of course there are other differences. For example, the ink produced by Factory A and the ink produced by Factory B are both between 20 and 28 microns in particle size, but the particle size distribution of ink produced by Factory A is concentrated around 24 microns, while that of ink produced by Factory B is between 20 and 28 microns.

4.In addition to the properties of these inks, we should also pay attention to the release of residual organic solvents in the plastic color printing industry, because the products from the color printing factory generally contact with food directly, although substances such as ink glue do not contact food directly, but some small molecular substances will still migrate to the surface of the film, affecting the hygiene of food, so there are corresponding national standards for countries with residual solvents. And color printing factories should also buy corresponding testing equipment, but at present, most small factories do not have such equipment, and many color printing factories with complete testing equipment in China do not strictly control this index, resulting in unsatisfactory product hygiene indicators.

5.Production technology is also a factor to be considered, but at present, the process level of each color printing factory is basically mature, and there is little difference, but it is particularly important to pay attention to the difference of printing machine speed. The printing speed between different color printing factories is about 80-250m/min. If the color printing factory wants to change the ink, it is necessary to consider the viscosity characteristics of the ink, especially the ink viscosity of ultra-high-speed printing (more than 200m/min) should be very low, and the color concentration should meet the standard.

Hue problems often encountered by ink color printing manufacturers:

1.There is color difference between inks of the same hue produced by different ink manufacturers. In the case that the printed patterns are not overlapped by inks of different colors, the color difference may not feel great, but if there are overlapped parts, the difference may be obvious. This requires the ink factory to make appropriate adjustments to the ink formula to minimize this difference. Increase the cost for the color printing factory, so we should also take this into account when changing the ink manufacturer.

2. Generally, the superposition of inks of different colors will occur due to screening, and there will be slight differences in hue without revision and unchanged process conditions. At the same time, due to the characteristics of color printing, most of the printing colors are more than 5 colors, reaching more than a dozen colors, including primary color ink and spot color ink, and other auxiliary printing materials, such as varnish, should be added according to special process requirements. Therefore, the application of spot-color ink in color printing factory is also very common. Spot-color ink is generally specially prepared by technicians of color printing factory. Under the condition that the printing plate and other technological conditions remain unchanged, the replaced ink can generally be close to the color sample of the original product. However, if the printing pattern is complex and the technology is special, it will often fail to meet the requirements of color sample. If so, the ink factory will adjust the ink formula or revise it. If the latter is the case, it will increase the cost for the color printing factory.

General process of changing ink (from a factory ink to b factory ink):

(1)First of all, the color samples of the primary color ink and spot color ink of Factory A are provided to Factory B. If it is printed matter, it is required that it has not been superimposed, and it is best to have a solid color block.

(2) There are multiple sets of plates in the color printing factory. First, one or several sets of plates are provided to the ink factory, and factory B is required to make proofing. Generally, the plates provided to Factory B are mainly selected from primary color ink blocks and commonly used spot color inks.

(3) When entering the experimental stage, technicians from the ink factory (proficient in printing process and ink performance) usually go to the site for debugging.

(4) In this process, there are mainly several primary color inks, and the commonly used spot color inks basically meet the requirements of the ink hue of Factory A, so the color printing factory can basically replace it with the ink of Factory B.

(5)Generally, the color printing factory has a more difficult version (more spot color inks), while the ink factory generally produces spot color inks. Therefore, the difficulty lies in the color difference between the printed samples and the standard samples when making such products. In the case that the primary color inks are basically the same, the color difference is generally caused by spot color inks. The specific analysis is as follows:

a.In the printed pattern, when the spot-color ink has no screening and overlapping colors, the spot-color ink has color difference, and the ink formula is generally readjusted by the ink factory. If this spot color ink is prepared by an ink factory, it is generally prepared by an ink factory (spot color ink is prepared from several inks).

b.In the case that the printed pattern is screened and there are inks with different hues superimposed, we should first analyze whether it is caused by the primary color ink or the spot color ink, and make adjustments according to E1. If it is caused by primary color ink, the ink factory should be required to adjust the formula of primary color ink; if it is caused by spot color ink, it should be adjusted according to E1.

c:There is a more special and complicated situation, that is, there are multiple hues overlapping in the pattern of a product, that is, there are several overlapping holes in the same plate. If the proofing results are inconsistent with the standard sample for the first time, some of the printed samples are consistent and the other parts are inconsistent, so pay attention to the analysis:

1. There are differences in hue among different ink manufacturers.
2. There are differences in shades between inks of the same color (sometimes it can be solved through revision).
The above briefly discusses the problems that color printing manufacturers often encounter when replacing ink, hoping to be helpful to related manufacturers, and I hope to discuss related issues with you!

Taking cigarette packets as an example, this paper analyzes the common problems and solutions of UV screen printing matte ink in the printing process.

Formation principle: The initial state of ink transferred from the printing plate to the substrate is uniformly distributed ink dots, which are not completely extended and connected together before entering the drying system, so the ink layer on the surface of the printed matter does not completely cover the surface of the substrate, resulting in small gaps like pinholes.

Main reasons:

1. Poor ink fluidity.

2. Ink is easy to produce bubbles in the printing process, which will lead to uneven distribution on the surface of ink after the bubbles burst.

Solution:

1. Try to remove the solid filler except sand powder from ink components to improve its fluidity.

2. Add UV thinner to dilute the ink and increase the fluidity.

3. Add a proper amount of defoamer and leveling agent to improve the printing effect.

Dry edge phenomenon

Formation principle: If the ink layer of printed matter is thick, there will be obvious "step" phenomenon in the printed area and blank area. Under the condition of the same scraper pressure, the actual pressure of the ink in the printing area will be greater than that in the blank area, while the UV screen printing matte ink has a strong matte feeling, a high content of sand powder and relatively large particles, so in the printing process, the edge position of the transition from the printing area to the blank area is prone to dry edge phenomenon.

Main reasons:

1. The sand powder particles are larger, the screen mesh number is higher and the mesh is smaller.

2. The pressure of scraper printing is insufficient. 3. The viscosity of ink is not enough, and its components are easy to disperse after being subjected to certain pressure.
Solution:

1. Choose ink with moderate sand particles and screen with moderate mesh number to match them.

2. Adjust the scraper pressure. 3. Adding resin components to the ink to enhance the integrity of the ink composition.
Shallow before and then deep, and the sand feeling is weak before and then strong

Formation principle: Screen printing, a unique printing method, determines that small-particle components such as monomers, resins and additives in ink components are easier to transfer to the substrate than large-particle components such as pigments and sand powder during printing, which makes the ink components on the screen inconsistent during the printing cycle from each ink addition to the next ink addition, resulting in the situation that the sand feeling changes from weak to strong and the ink color changes from shallow to deep.

Main reasons :

1. The solid content of ink is high, the components are not easy to form a whole, and the components are separated quickly.

2. The printing characteristics of screen printing determine.
Solution:

1. Add resin liquid to the ink to make the components of the ink form a whole as much as possible and transfer them evenly to the substrate. 2. Add automatic ink adding and ink returning system to the equipment, and shorten the cycle as much as possible.
Paste word phenomenon

Formation principle: During the period from the transfer of ink to the substrate to the thorough drying in the drying system, due to its poor fluidity, the printed small characters will be slightly smaller than the actual size of the print plate, resulting in unclear characters.
Main reason: the fluidity of ink itself is unstable.
Solution:

1. When the ink viscosity is determined, enlarge the actual size of the print plate according to the actual printing situation.

2. Thicken the ink when the actual print size is determined.

In addition to the above common problems, there are other quality problems in the printing process of screen-printed UV matte ink, which requires operators to learn and use it flexibly, analyze the reasons reasonably, find solutions and summarize them in time, and constantly accumulate experience to improve their technical level.

Welcome friends from the glass printing factory to consult Screen Printing Ink or Screen Printing Machine via email :yan@lauerink.com or whatsapp:86-18022025378